1. Field of the Invention
The invention relates to a fuel injection apparatus for internal combustion engines in which fuel is conveyed from a high-pressure fuel source to an injection opening via a control valve.
2. Description of the Prior Art
In fuel injection apparatuses of the kind referred to above, which are extensively known from the prior art and are particularly used in common rail systems, the supply of fuel to the injection opening, which is usually embodied as a nozzle holder device, is frequently controlled by means of a slide valve or seat/slide valve, which can be embodied as force-compensated or partially force-compensated. The use of slide valves, which have control edges for covering and uncovering inlets and outlets, however, is disadvantageous due to the large leakages, which result from the usually small overlap.
One way to avoid these disadvantages is to use a double seat valve, which has the advantage over slide valves that the stroke length is considerably increased and in which a high degree of sealing action at the seats can be achieved. In trials, it has also been demonstrated that the stroke length in a double seat valve can be selected to be small so that the valve can be directly controlled by a piezoelectric unit while complying with the requirement for a force-compensated valve.
DE 198 60 678 has disclosed a fuel injection apparatus for internal combustion engines of this kind in which a fuel injection valve is supplied with fuel by means of a pressure line. For controlling an injection opening, this known fuel injection apparatus has an injection valve member whose movementxe2x80x94and therefore the opening of the injection nozzlexe2x80x94is controlled by a control valve, which has a control valve member that is actuated by the piezoelectric actuator. This control valve member is embodied with a valve head and cooperates with two valve seats of the control valve in such a way that when electrical voltage is applied to the piezoelectric actuator, this permits a flow of fuel, which is conveyed from the high-pressure fuel source by means of a line, via the first valve seat and the second valve seat, and into a line leading to the injection opening.
However, the complex embodiment of the valve housing with a number of mold joints has proven to be problematic, where it turns out to be particularly difficult to assemble a force-compensated valve with a multi-part valve body.
The fuel injection apparatus according to the invention has the advantage that the control valve is provided as a precisely functioning 3/2-way valve in a pressure-controlled system, which valve can be directly actuated by a piezoelectric unit by means of a mechanical transmission and in a particularly advantageous manner, by means of a hydraulic transmission. The integration of the control valve into the inlet of fuel into the injection opening of the fuel injection apparatus permits short injections that can be precisely metered.
A significant advantage of the fuel injection apparatus according to the invention lies in the design of the control valve, which permits the realization of the valve with essentially one valve body into which a component that is suitable for embodying the second valve seat and the second guide can be inserted, preferably a sleeve.
Embodied in a correspondingly simple manner, the assembly of the control valve, particularly the valve body and the opposing piece that constitutes the second valve seat can be advantageously produced in one chucking operation. This achieves a high degree of precision fit of the components with one another.